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                <h2 id="Introducing-Combine"><a href="#Introducing-Combine" class="headerlink" title="Introducing Combine"></a>Introducing Combine</h2><p>Asynchronous Interfaces</p>
<ul>
<li>Target/Action</li>
<li>Notification center</li>
<li>URLSession</li>
<li>Key-value observable</li>
<li>Ad-hoc callbacks</li>
</ul>
<p>A unified, declarative API for<br>processing values over time (一个统一的,申明式的API处理数据随着)</p>
<h2 id="Combine-Features"><a href="#Combine-Features" class="headerlink" title="Combine Features"></a>Combine Features</h2><p>Combine基于Swift编写的框架,所以包含了一些Swift的语言的语法特性</p>
<h3 id="Generic"><a href="#Generic" class="headerlink" title="Generic"></a>Generic</h3><p>泛性支持,可以进行类型约束,定义更多的模版代码,但过量的泛性会导致代码的可读性变差</p>
<h3 id="Type-Safe"><a href="#Type-Safe" class="headerlink" title="Type Safe"></a>Type Safe</h3><p>类型安全约束,同样受惠于 Swift，可以让编译器和 Runtime 帮助我们检查类型安全问题。</p>
<h3 id="Composition-first"><a href="#Composition-first" class="headerlink" title="Composition first"></a>Composition first</h3><p>组合优先,将多个异步数据源组合到一起</p>
<h3 id="Request-Driven"><a href="#Request-Driven" class="headerlink" title="Request Driven"></a>Request Driven</h3><p>请求驱动: 消费者向生产者请求某个事务变化,当变化时生产者给消费者对应的响应<br>不同于事件驱动: 基于事件通知的设计思想。在事务发生变化时，生产者将通知提交给事件管道进行分发，而不关心谁去消费事件。消费者需要到事件管道中订阅关心的通知。</p>
<h2 id="Combine的核心"><a href="#Combine的核心" class="headerlink" title="Combine的核心"></a>Combine的核心</h2><h3 id="Publisher"><a href="#Publisher" class="headerlink" title="Publisher"></a>Publisher</h3><p>发布者: 生产数据</p>
<figure class="highlight swift"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">@available</span>(<span class="keyword">macOS</span> <span class="number">10.15</span>, <span class="keyword">iOS</span> <span class="number">13.0</span>, <span class="keyword">tvOS</span> <span class="number">13.0</span>, <span class="keyword">watchOS</span> <span class="number">6.0</span>, <span class="operator">*</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">protocol</span> <span class="title">Publisher</span> </span>{</span><br><span class="line"></span><br><span class="line">    <span class="comment">/// The kind of values published by this publisher.</span></span><br><span class="line">    <span class="keyword">associatedtype</span> <span class="type">Output</span></span><br><span class="line"></span><br><span class="line">    <span class="comment">/// The kind of errors this publisher might publish.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// Use `Never` if this `Publisher` does not publish errors.</span></span><br><span class="line">    <span class="keyword">associatedtype</span> <span class="type">Failure</span> : <span class="type">Error</span></span><br><span class="line"></span><br><span class="line">    <span class="comment">/// Attaches the specified subscriber to this publisher.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// Implementations of ``Publisher`` must implement this method.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// The provided implementation of ``Publisher/subscribe(_:)-4u8kn``calls this method.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// - Parameter subscriber: The subscriber to attach to this ``Publisher``, after which it can receive values.</span></span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">receive</span>&lt;<span class="type">S</span>&gt;(<span class="params">subscriber</span>: <span class="type">S</span>)</span> <span class="keyword">where</span> <span class="type">S</span> : <span class="type">Subscriber</span>, <span class="keyword">Self</span>.<span class="type">Failure</span> <span class="operator">==</span> <span class="type">S</span>.<span class="type">Failure</span>, <span class="keyword">Self</span>.<span class="type">Output</span> <span class="operator">==</span> <span class="type">S</span>.<span class="type">Input</span></span><br><span class="line">    </span><br><span class="line">    <span class="comment">/// 为每个下游的订阅者单独创建一个subject</span></span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">multicast</span>&lt;<span class="type">S</span>&gt;(<span class="keyword">_</span> <span class="params">createSubject</span>: <span class="keyword">@escaping</span> () -&gt; <span class="type">S</span>)</span> -&gt; <span class="type">Publishers</span>.<span class="type">Multicast</span>&lt;<span class="keyword">Self</span>, <span class="type">S</span>&gt; <span class="keyword">where</span> <span class="type">S</span> : <span class="type">Subject</span>, <span class="keyword">Self</span>.<span class="type">Failure</span> <span class="operator">==</span> <span class="type">S</span>.<span class="type">Failure</span>, <span class="keyword">Self</span>.<span class="type">Output</span> <span class="operator">==</span> <span class="type">S</span>.<span class="type">Output</span></span><br><span class="line">    <span class="comment">/// 为每个下游订阅者共享一个subject</span></span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">multicast</span>&lt;<span class="type">S</span>&gt;(<span class="params">subject</span>: <span class="type">S</span>)</span> -&gt; <span class="type">Publishers</span>.<span class="type">Multicast</span>&lt;<span class="keyword">Self</span>, <span class="type">S</span>&gt; <span class="keyword">where</span> <span class="type">S</span> : <span class="type">Subject</span>, <span class="keyword">Self</span>.<span class="type">Failure</span> <span class="operator">==</span> <span class="type">S</span>.<span class="type">Failure</span>, <span class="keyword">Self</span>.<span class="type">Output</span> <span class="operator">==</span> <span class="type">S</span>.<span class="type">Output</span></span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>

<h3 id="Subscriber"><a href="#Subscriber" class="headerlink" title="Subscriber"></a>Subscriber</h3><p>订阅者: 定义了如何描述接受的值和错误，类似的，通过定义关联类型 Input 和 Failure。由于订阅者在接受到值之后，经常会影响和修改某些状态，所以我们使用引用类型来定义它，也就是 Swift 里的类类型。</p>
<figure class="highlight swift"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">@available</span>(<span class="keyword">macOS</span> <span class="number">10.15</span>, <span class="keyword">iOS</span> <span class="number">13.0</span>, <span class="keyword">tvOS</span> <span class="number">13.0</span>, <span class="keyword">watchOS</span> <span class="number">6.0</span>, <span class="operator">*</span>)</span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">protocol</span> <span class="title">Subscriber</span> : <span class="title">CustomCombineIdentifierConvertible</span> </span>{</span><br><span class="line"></span><br><span class="line">    <span class="comment">/// The kind of values this subscriber receives.</span></span><br><span class="line">    <span class="keyword">associatedtype</span> <span class="type">Input</span></span><br><span class="line"></span><br><span class="line">    <span class="comment">/// The kind of errors this subscriber might receive.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// Use `Never` if this `Subscriber` cannot receive errors.</span></span><br><span class="line">    <span class="keyword">associatedtype</span> <span class="type">Failure</span> : <span class="type">Error</span></span><br><span class="line"></span><br><span class="line">    <span class="comment">/// Tells the subscriber that it has successfully subscribed to the publisher and may request items.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// Use the received ``Subscription`` to request items from the publisher.</span></span><br><span class="line">    <span class="comment">/// - Parameter subscription: A subscription that represents the connection between publisher and subscriber.</span></span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">receive</span>(<span class="params">subscription</span>: <span class="type">Subscription</span>)</span></span><br><span class="line"></span><br><span class="line">    <span class="comment">/// Tells the subscriber that the publisher has produced an element.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// - Parameter input: The published element.</span></span><br><span class="line">    <span class="comment">/// - Returns: A `Subscribers.Demand` instance indicating how many more elements the subscriber expects to receive.</span></span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">receive</span>(<span class="keyword">_</span> <span class="params">input</span>: <span class="keyword">Self</span>.<span class="type">Input</span>)</span> -&gt; <span class="type">Subscribers</span>.<span class="type">Demand</span></span><br><span class="line"></span><br><span class="line">    <span class="comment">/// Tells the subscriber that the publisher has completed publishing, either normally or with an error.</span></span><br><span class="line">    <span class="comment">///</span></span><br><span class="line">    <span class="comment">/// - Parameter completion: A ``Subscribers/Completion`` case indicating whether publishing completed normally or with an error.</span></span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">receive</span>(<span class="params">completion</span>: <span class="type">Subscribers</span>.<span class="type">Completion</span>&lt;<span class="keyword">Self</span>.<span class="type">Failure</span>&gt;)</span></span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>

<h3 id="Operator"><a href="#Operator" class="headerlink" title="Operator"></a>Operator</h3><p>运算符: 当有了发布者和订阅者后,他们之间会通过请和**订阅(Subscription)**的方式关联起来</p>
<figure class="highlight plain"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br></pre></td><td class="code"><pre><span class="line">sequenceDiagram</span><br><span class="line">participant Publisher</span><br><span class="line">   participant Subscriber</span><br><span class="line"></span><br><span class="line">  </span><br><span class="line">   Subscriber -&gt;&gt; Publisher:1.subscribe</span><br><span class="line">   Publisher -&gt;&gt; Subscriber:2.receive(subscription:)</span><br><span class="line">   Subscriber -&gt;&gt; Publisher:3.request(_ :Demand)</span><br><span class="line">   loop workflow </span><br><span class="line">   Publisher -&gt;&gt; Subscriber:4.receive(_ :Input)</span><br><span class="line">   Subscriber -&gt;&gt; Publisher:5.update(_ :Demand)</span><br><span class="line">   </span><br><span class="line">   activate Publisher</span><br><span class="line">   Note over Publisher,Subscriber: .&lt;br&gt;.&lt;br&gt;</span><br><span class="line">   deactivate Publisher</span><br><span class="line">   end</span><br><span class="line"></span><br><span class="line">   Publisher -&gt;&gt; Subscriber:6.receive(completion:)</span><br><span class="line">       </span><br></pre></td></tr></tbody></table></figure>

<p>下面是一个小例子</p>
<figure class="highlight swift"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">var</span> result <span class="operator">=</span> <span class="type">Result</span>()</span><br><span class="line"><span class="keyword">let</span> pub2 <span class="operator">=</span> [<span class="string">"First"</span>, <span class="string">"Second"</span>, <span class="string">"Third"</span>].publisher.append(<span class="string">"Four"</span>)</span><br><span class="line">    .map( { <span class="keyword">return</span> (<span class="variable">$0</span>, <span class="type">Int</span>.random(in: <span class="number">0</span><span class="operator">...</span><span class="number">100</span>)) } )</span><br><span class="line">    .print(<span class="string">"Random"</span>) <span class="comment">//会执行很多很多次</span></span><br><span class="line">    .multicast(subject: <span class="type">PassthroughSubject</span>&lt;(<span class="type">String</span>,<span class="type">Int</span>),<span class="type">Never</span>&gt;())</span><br><span class="line">pub2.receive(subscriber: <span class="type">Subscribers</span>.<span class="type">Assign</span>(object: result, keyPath: \.value))</span><br><span class="line">pub2.connect()</span><br><span class="line"> </span><br><span class="line"><span class="built_in">print</span>(<span class="string">"========="</span>)</span><br><span class="line"><span class="built_in">print</span>(result.value)</span><br><span class="line"></span><br><span class="line"><span class="comment">/// Log</span></span><br><span class="line"><span class="type">Random</span>: receive subscription: ([(<span class="string">"First"</span>, <span class="number">26</span>), (<span class="string">"Second"</span>, <span class="number">88</span>), (<span class="string">"Third"</span>, <span class="number">72</span>), (<span class="string">"Four"</span>, <span class="number">64</span>)])</span><br><span class="line"><span class="type">Random</span>: request unlimited</span><br><span class="line"><span class="type">Random</span>: receive value: ((<span class="string">"First"</span>, <span class="number">26</span>))</span><br><span class="line"><span class="type">Random</span>: receive value: ((<span class="string">"Second"</span>, <span class="number">88</span>))</span><br><span class="line"><span class="type">Random</span>: receive value: ((<span class="string">"Third"</span>, <span class="number">72</span>))</span><br><span class="line"><span class="type">Random</span>: receive value: ((<span class="string">"Four"</span>, <span class="number">64</span>))</span><br><span class="line"><span class="type">Random</span>: receive finished</span><br><span class="line"><span class="operator">=========</span></span><br><span class="line">(<span class="string">"Four"</span>, <span class="number">64</span>)</span><br></pre></td></tr></tbody></table></figure>

<h3 id="Combine框架中的操作符"><a href="#Combine框架中的操作符" class="headerlink" title="Combine框架中的操作符"></a>Combine框架中的操作符</h3><h4 id="函数式转换"><a href="#函数式转换" class="headerlink" title="函数式转换"></a>函数式转换</h4><p>map,filter,reduce</p>
<h4 id="列表操作"><a href="#列表操作" class="headerlink" title="列表操作"></a>列表操作</h4><p>first,drop,append</p>
<h4 id="错误处理"><a href="#错误处理" class="headerlink" title="错误处理"></a>错误处理</h4><p>catch, retry</p>
<h4 id="线程-队列行为"><a href="#线程-队列行为" class="headerlink" title="线程/队列行为"></a>线程/队列行为</h4><p>subscribeOne,receiveOn</p>
<h4 id="调度和时间处理"><a href="#调度和时间处理" class="headerlink" title="调度和时间处理"></a>调度和时间处理</h4><p>delay,debounce</p>
<h2 id="Combine设计理念"><a href="#Combine设计理念" class="headerlink" title="Combine设计理念"></a>Combine设计理念</h2><p>优先是使用组合。</p>
<table>
<thead>
<tr>
<th></th>
<th>Synchronous</th>
<th>Asynchronous</th>
</tr>
</thead>
<tbody><tr>
<td>One</td>
<td>Int</td>
<td>Future</td>
</tr>
<tr>
<td>Manay</td>
<td>Array</td>
<td>Publisher</td>
</tr>
</tbody></table>
<h3 id="组合多个发布者"><a href="#组合多个发布者" class="headerlink" title="组合多个发布者"></a>组合多个发布者</h3><figure class="highlight plain"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"></span><br><span class="line">graph TD;</span><br><span class="line"></span><br><span class="line">A[PublisherA]--&gt;C</span><br><span class="line">B[PublisherB]--&gt;C</span><br><span class="line">C[Zip]</span><br><span class="line">C---D</span><br><span class="line">D(value1,value2)</span><br><span class="line">D--&gt;E</span><br><span class="line">E[Subscriber]</span><br></pre></td></tr></tbody></table></figure>

<figure class="highlight swift"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">extension</span> <span class="title">Publishers</span> </span>{</span><br><span class="line">    <span class="keyword">public</span> <span class="class"><span class="keyword">struct</span> <span class="title">Zip</span>&lt;<span class="title">A</span>, <span class="title">B</span>&gt; : <span class="title">Publisher</span> <span class="title">where</span> <span class="title">A</span> : <span class="title">Publisher</span>, <span class="title">B</span> : <span class="title">Publisher</span>, <span class="title">A</span>.<span class="title">Failure</span> == <span class="title">B</span>.<span class="title">Failure</span> </span>{</span><br><span class="line">        <span class="keyword">public</span> <span class="keyword">typealias</span> <span class="type">Output</span> <span class="operator">=</span> (<span class="type">A</span>.<span class="type">Output</span>, <span class="type">B</span>.<span class="type">Output</span>)</span><br><span class="line">        <span class="keyword">public</span> <span class="keyword">typealias</span> <span class="type">Failure</span> <span class="operator">=</span> <span class="type">A</span>.<span class="type">Failure</span></span><br><span class="line">        <span class="keyword">public</span> <span class="keyword">let</span> a: <span class="type">A</span></span><br><span class="line">        <span class="keyword">public</span> <span class="keyword">let</span> b: <span class="type">B</span></span><br><span class="line">        <span class="keyword">public</span> <span class="function"><span class="keyword">init</span>(<span class="keyword">_</span> <span class="params">a</span>: <span class="type">A</span>, <span class="keyword">_</span> <span class="params">b</span>: <span class="type">B</span>)</span></span><br><span class="line">        <span class="keyword">public</span> <span class="function"><span class="keyword">func</span> <span class="title">receive</span>&lt;<span class="type">S</span>&gt;(<span class="params">subscriber</span>: <span class="type">S</span>)</span> <span class="keyword">where</span> <span class="type">S</span> : <span class="type">Subscriber</span>, <span class="type">B</span>.<span class="type">Failure</span> <span class="operator">==</span> <span class="type">S</span>.<span class="type">Failure</span>, <span class="type">S</span>.<span class="type">Input</span> <span class="operator">==</span> (<span class="type">A</span>.<span class="type">Output</span>, <span class="type">B</span>.<span class="type">Output</span>)</span><br><span class="line">    }</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>

<h3 id="监听最新的发布数据"><a href="#监听最新的发布数据" class="headerlink" title="监听最新的发布数据"></a>监听最新的发布数据</h3><figure class="highlight plain"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">graph TD;</span><br><span class="line"></span><br><span class="line">A[PublisherA]--&gt;C</span><br><span class="line">B[PublisherB]--&gt;C</span><br><span class="line">C[CombineLatest value1,value2]--&gt;D</span><br><span class="line">D[Subscriber]</span><br><span class="line"></span><br></pre></td></tr></tbody></table></figure>

<h2 id="Combine-实例"><a href="#Combine-实例" class="headerlink" title="Combine 实例"></a>Combine 实例</h2><p>通过将异步的网络请求转换为<code>AnyObserver</code>提供给对应的订阅者</p>
<figure class="highlight swift"><table><tbody><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">StringDecoder</span>: <span class="title">TopLevelDecoder</span> </span>{</span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">decode</span>&lt;<span class="type">T</span>&gt;(<span class="keyword">_</span> <span class="params">type</span>: <span class="type">T</span>.<span class="keyword">Type</span>, <span class="params">from</span>: <span class="type">Data</span>)</span> <span class="keyword">throws</span> -&gt; <span class="type">T</span> <span class="keyword">where</span> <span class="type">T</span> : <span class="type">Decodable</span> {</span><br><span class="line">        <span class="keyword">return</span> <span class="type">String</span>(data: from, encoding: <span class="type">String</span>.<span class="type">Encoding</span>.utf8) <span class="keyword">as!</span> <span class="type">T</span></span><br><span class="line">    }</span><br><span class="line">    </span><br><span class="line">    <span class="keyword">typealias</span> <span class="type">Input</span> <span class="operator">=</span> <span class="type">Data</span></span><br><span class="line">}</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">WatchNetWorking</span> </span>{</span><br><span class="line">    <span class="keyword">static</span> <span class="keyword">let</span> shared <span class="operator">=</span> <span class="type">WatchNetWorking</span>()</span><br><span class="line">   </span><br><span class="line">     </span><br><span class="line">    <span class="keyword">var</span> url: <span class="type">String</span> {</span><br><span class="line">        <span class="keyword">return</span> <span class="string">"https://www.baidu.com"</span></span><br><span class="line">    }</span><br><span class="line">    </span><br><span class="line">    <span class="function"><span class="keyword">func</span> <span class="title">fetchData</span>()</span> -&gt; <span class="type">AnyPublisher</span>&lt;<span class="type">String</span>,<span class="type">ExampleError</span>&gt; {</span><br><span class="line">        <span class="keyword">guard</span> <span class="keyword">let</span> _url <span class="operator">=</span> <span class="type">URL</span>.<span class="keyword">init</span>(string: url) <span class="keyword">else</span> {</span><br><span class="line">            <span class="keyword">return</span> <span class="type">Fail</span>&lt;<span class="type">String</span>,<span class="type">ExampleError</span>&gt;(error: <span class="type">ExampleError</span>.dataParserError).eraseToAnyPublisher()</span><br><span class="line">        }</span><br><span class="line">      </span><br><span class="line">        <span class="keyword">return</span> <span class="type">URLSession</span>.shared.dataTaskPublisher(for: _url)</span><br><span class="line">            .tryMap { (data: <span class="type">Data</span>, response: <span class="type">URLResponse</span>) -&gt; <span class="type">Data</span> <span class="keyword">in</span></span><br><span class="line">                <span class="keyword">guard</span> <span class="keyword">let</span> httpResponse <span class="operator">=</span> response <span class="keyword">as?</span> <span class="type">HTTPURLResponse</span>, <span class="number">200</span><span class="operator">...</span><span class="number">299</span> <span class="operator">~=</span> httpResponse.statusCode <span class="keyword">else</span> {</span><br><span class="line">                    <span class="keyword">throw</span> <span class="type">ExampleError</span>.apiError((response <span class="keyword">as?</span> <span class="type">HTTPURLResponse</span>)<span class="operator">?</span>.statusCode <span class="operator">??</span> <span class="number">500</span>)</span><br><span class="line">                }</span><br><span class="line">                <span class="keyword">return</span> data</span><br><span class="line">            }.decode(type: <span class="type">String</span>.<span class="keyword">self</span>, decoder: <span class="type">StringDecoder</span>())</span><br><span class="line">            .mapError({ (error) -&gt; <span class="type">ExampleError</span> <span class="keyword">in</span></span><br><span class="line">                <span class="keyword">switch</span> (error) {</span><br><span class="line">                <span class="keyword">case</span> <span class="keyword">is</span> URLError:</span><br><span class="line">                 <span class="keyword">return</span> <span class="type">ExampleError</span>.apiError(<span class="operator">-</span><span class="number">9999</span>)</span><br><span class="line">                default:</span><br><span class="line">                    <span class="keyword">return</span> <span class="type">ExampleError</span>.customError</span><br><span class="line">                }</span><br><span class="line">            })</span><br><span class="line">            .eraseToAnyPublisher()</span><br><span class="line">        </span><br><span class="line">    }</span><br><span class="line">}</span><br></pre></td></tr></tbody></table></figure>

<p>数据处理流程: </p>
<p>请求参数拼接 -》 有效性校验 -》发起网络请求 -》错误处理 -》 数据转换 -》解码 –》转换为限定类型的AnyPublisher</p>
<h2 id="参考连接"><a href="#参考连接" class="headerlink" title="参考连接"></a>参考连接</h2><p><a target="_blank" rel="noopener" href="https://github.com/CombineCommunity/rxswift-to-combine-cheatsheet">RxSwift Vs Combine</a></p>
<p><a target="_blank" rel="noopener" href="https://xiaozhuanlan.com/topic/8362954017">WWDCC 19专栏</a><br><a target="_blank" rel="noopener" href="https://developer.apple.com/videos/play/wwdc2019/722/">Apple Introducing Combine</a></p>
<p><a target="_blank" rel="noopener" href="https://github.com/apple/swift/blob/main/stdlib/public/Darwin/Foundation/Publishers+NotificationCenter.swift">Publishers+NotificationCenter.swift</a></p>
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